A coaxial resonator includes a cavity such as a rectangularly shaped cavity, and the cavity's fundamental frequency, referred to as f.sub.o, is usually set by selecting the relationship between a center conductor and the center conductor's closing cover (cap) which are disposed within the cavity. The closing cover and the opposite wall of the resonator cavity constitute the plates of a capacitor. The RF input signal, which is input to the cavity, produces an electric field between these capacitor plates and a magnetic field that is orthogonal to the electric field with maximum strength around the center conductor. The resonator's fundamental frequency is strongly determined by the center conductor's closing cover. The area of the closing cover determines the capacitance. The resonator is usually tuned, i.e., the resonator's fundamental frequency is selected, by adjusting the length of the center conductor, thereby changing the capacitance. This tuning is usually accomplished indirectly by moving an adjustment screw disposed in opposition to the center conductor. A pick-up loop, which is usually situated on one of the resonator's walls, is provided in the resonator. The loop picks up the tuned signal frequency (for setting the resonator, this frequency is the desired f.sub.o).
A problem with the above-described conventional coaxial resonators is the difficulty of adjustment over a wide RF-bandwidth, e.g., 10 megahertz (MHz) around a center frequency of 465 MHz. Such wideband operation in connection with common adjustment means normally requires the use of bulky resonators. In a typical cellular telephone base station, there are, for example, eight resonators each handling two channels. If not all the resonators are used in the system, it is necessary to park the frequency for the unused resonators outside the active frequency band in order not to disturb other channels. The bulkiness and associated adjustment arrangements for the conventional resonators are so unsatisfactory, that there is a need for an entirely new design in order to alleviate the bulkiness associated with conventional designs.